System and Method for Measuring Current of an Electrosurgical Generator

ABSTRACT

An electrosurgical generator includes an RF output stage, a DC blocking capacitor, a measuring circuit, and a sensor circuit. The RF output stage generates electrosurgical energy for application to an active electrode. The DC blocking capacitor is electrically coupled between the RF output stage and the active electrode. The measuring circuit is coupled to the DC blocking capacitor and measures the voltage across the DC blocking capacitor. The sensor circuit determines the current of the electrosurgical energy as a function of the voltage across the DC blocking capacitor.

BACKGROUND

1. Technical Field

The present disclosure relates to a system and method for performingelectrosurgical procedures. More particularly, the present disclosurerelates to a system and method for measuring current of anelectrosurgical generator using the voltage across a DC blockingcapacitor.

2. Background of Related Art

Electrosurgery involves application of radio frequency electricalcurrent (e.g., electrosurgical energy) to a surgical site to cut,ablate, coagulate, or seal tissue. In electrosurgery, a source or activeelectrode delivers electrosurgical energy from the electrosurgicalgenerator to the tissue and a return electrode carries the current backto the generator. In monopolar electrosurgery, the source electrode istypically part of the surgical instrument held by the surgeon and isapplied to the tissue to be treated. In bipolar electrosurgery, thereturn electrode is part of a patient return pad positioned remotelyfrom the active electrode on the patient's body to carry the currentback to the generator.

Ablation is a monopolar procedure which is particularly useful in thefield of neurosurgery and cancer tumor hyperthermia, where one or moreRF ablation needle electrodes (usually of elongated cylindricalgeometry) are inserted into a living body. A typical form of such needleelectrodes incorporates an insulated sheath from which an exposed(uninsulated) tip extends. When RF energy is provided between the returnelectrode and the inserted ablation electrode, RF current flows from theneedle electrode through the body. Typically, the current density isvery high near the tip of the needle electrode, which tends to heat anddestroy surrounding tissue.

In bipolar electrosurgery, one of the electrodes of the hand-heldinstrument functions as the active electrode and the other as the returnelectrode. The return electrode is placed in close proximity to theactive electrode such that an electrical circuit is formed between thetwo electrodes (e.g., electrosurgical forceps). In this manner, theapplied electrical current is limited to the body tissue positionedbetween the electrodes. When the electrodes are sufficiently separatedfrom one another, the electrical circuit is open and thus inadvertentcontact with body tissue with either of the separated electrodes doesnot cause current to flow.

SUMMARY

In one embodiment of the present disclosure, an electrosurgicalgenerator is adapted to supply the energy to the at least one activeelectrode. The electrosurgical generator includes an RF output stage, aDC blocking capacitor, a measuring circuit, and a sensor circuit. The RFoutput stage generates the electrosurgical energy. The DC blockingcapacitor is electrically coupled between the RF output stage andtissue. The electrosurgical generator can detect a fault of the DCblocking capacitor. The measuring circuit is coupled to the DC blockingcapacitor and measures the voltage across the DC blocking capacitor. Thesensor circuit determines the current of the electrosurgical energy as afunction of the voltage across the DC blocking capacitor. In someembodiments of the present disclosure, the system determines the currentof the electrosurgical energy in an absence of a current sensetransformer to measure the current of the electrosurgical energy. Any ofthe embodiments disclosed herein of the electrosurgical generator may beused with an electrosurgical system. In an embodiment of the presentdisclosure, the electrosurgical generator may be used with anelectrosurgical system that includes an electrosurgical instrument andthe electrosurgical generator. The electrosurgical instrument includesat least one active electrode adapted to apply electrosurgical energy totissue.

In an embodiment of the present disclosure, the generator furtherincludes a first, second, third, and fourth capacitor. The DC blockingcapacitor has first and second nodes and each of the first, second,third, and fourth capacitors has respective first and second nodes. Thefirst capacitor's first node is coupled to the first node of the DCblocking capacitor. The second capacitor's first node is coupled betweenthe second node of the first capacitor and a reference (e.g., ground).The third capacitor's first node is coupled to the second node of the DCblocking capacitor. The fourth capacitor's first node is coupled betweenthe second node of the third capacitor and the reference. The sensorcircuit may be coupled to the second node of the first capacitor and thesecond node of the third capacitor to determine the voltage therebetweento determine the current of the electrosurgical energy as a function ofthe voltage across the DC blocking capacitor.

In one embodiment of the present disclosure, the first capacitor has acapacitance that is about equal to a capacitance of the third capacitor.The second capacitor may have a capacitance that is about equal to thecapacitance of the fourth capacitor.

In yet another embodiment of the present disclosure, the sensor circuitdetermines the current utilizing the relationship of: I=C(dv/dt). C isan estimated capacitance of the DC blocking capacitor, dv is the measureof the voltage across the DC blocking capacitor, and dt is apredetermined interval of the electrosurgical energy. The DC blockingcapacitor may have a capacitance of around 50 nF for bipolar energy and5 nF for monopolar energy.

In another embodiment of the present disclosure, an electrosurgicalgenerator includes an RF output stage, a DC blocking capacitor, andmeasuring and sensor circuits. The RF output stage generateselectrosurgical energy for application to an active electrode. The DCblocking capacitor is electrically coupled between the RF output stageand the active electrode. The measuring circuit is coupled to the DCblocking capacitor to measure the voltage across the DC blockingcapacitor. The sensor circuit determines the current of theelectrosurgical energy as a function of the voltage across the DCblocking capacitor.

In an embodiment of the present disclosure, the electrosurgicalgenerator includes fifth and sixth capacitors. The fifth capacitor isconnected in series or in parallel with the first capacitor. The sixthcapacitor is connected in series or in parallel with the thirdcapacitor.

In another embodiment of the present disclosure, the electrosurgicalgenerator includes a cut-off circuit. The cut-off circuit is coupled tothe sensor circuit to communicate the determined current of theelectrosurgical therefrom, wherein the cut-off circuit is adapted tostop the application of the electrosurgical energy to the activeelectrode when the measured current reaches a predetermined threshold.The electrosurgical generator may further include a switch coupledbetween the RF output stage and the active electrode. The cut-offcircuit includes a comparator to compare the determined current to thepredetermined threshold and to generate a cut-off signal adapted tosignal the switch to stop the application of the electrosurgical energyto the active electrode.

In an embodiment of the present disclosure, a return electrode isadapted to return the electrosurgical energy. An another DC blockingcapacitor is electrically coupled between the RF output stage and thereturn electrode. An another measuring circuit is coupled to the anotherDC blocking capacitor to measure the voltage across the another DCblocking capacitor. The sensor circuit determines the current of thereturn electrosurgical energy as a function of the voltage across theanother DC blocking capacitor. A leakage current measuring circuit iscoupled to the sensor to compare the current of the electrosurgicalenergy to the current of the return electrosurgical energy to measure aleakage current.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1 is a schematic block diagram of an electrosurgical systemaccording to the present disclosure;

FIG. 2 is a schematic block diagram of an electrosurgical generatoraccording to the present disclosure;

FIG. 3 shows a circuit coupled to a DC blocking capacitor that may beused by the generator of FIG. 1 or 2 according to the presentdisclosure; and

FIG. 4 shows a circuit coupled to a DC blocking capacitor and aredundant DC blocking capacitor for determining the current of theelectrosurgical energy according to the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail to avoid obscuring the present disclosure inunnecessary detail. Those skilled in the art will understand that theinvention according to the present disclosure may be adapted for usewith either monopolar or bipolar electrosurgical systems. FIG. 1 is aschematic illustration of an electrosurgical system according to thepresent disclosure. The system includes an electrosurgical instrument 10having one or more electrodes for treating tissue of a patient P. Theinstrument 10 may be either of monopolar type including one or moreactive electrodes (e.g., electrosurgical cutting probe, ablationelectrode(s), etc.) or of bipolar type including one or more active andreturn electrodes (e.g., electrosurgical sealing forceps).Electrosurgical RF energy is supplied to the instrument 10 by agenerator 20 via a supply line 12, which is operably connected to anactive output terminal, allowing the instrument 10 to coagulate, seal,ablate and/or otherwise treat tissue.

If the instrument 10 is of monopolar type then energy may be returned tothe generator 20 through a return electrode (not explicitly shown) whichmay be one or more electrode pads disposed on the patient's body. Thesystem may include a plurality of return electrodes which are believedto minimize the chances of tissue damage by maximizing the overallcontact area with the patient P. In addition, the generator 20 and themonopolar return electrode may be configured for monitoring thesufficiency of the so called “tissue-to-patient” contact impedance tofurther minimize chances of tissue damage.

If the instrument 10 is of bipolar type, the return electrode isdisposed in proximity to the active electrode (e.g., on opposing jaws ofbipolar forceps). The generator 20 may include a plurality of supply andreturn terminals and a corresponding number of electrode leads.

The generator 20 includes input controls (e.g., buttons, activators,switches, touch screen, etc.) for controlling the generator 20. Inaddition, the generator 20 may include one or more display screens forproviding the surgeon with variety of output information (e.g.,intensity settings, treatment complete indicators, etc.). The controlsallow the surgeon to adjust power of the RF energy, waveform, and otherparameters to achieve a waveform suitable for a particular task (e.g.,coagulating, tissue sealing, intensity setting, etc.). The instrument 10may also include a plurality of input controls redundant with certaininput controls of the generator 20. Redundant input controls on theinstrument 10 allow for easier and faster modification of RF energyparameters during the surgical procedure without requiring interactionwith the generator 20.

FIG. 2 shows a schematic block diagram of the generator 20 having asensor circuit 21, a cut-off circuit 22, a leakage current measuringcircuit 23, a controller 24, a high voltage DC power supply 27 (“HVPS”)and an RF output stage 28. The HVPS 27 provides high voltage DC power toan RF output stage 28 which then converts high voltage DC power into RFenergy and delivers the RF energy to the active electrode of theinstrument 10. In particular, the RF output stage 28 generatessinusoidal waveforms of high frequency RF energy. The RF output stage 28is configured to generate a plurality of waveforms having various dutycycles, peak voltages, crest factors, and other parameters. Certaintypes of waveforms are suitable for specific electrosurgical modes. Forinstance, the RF output stage 28 generates a 100% duty cycle sinusoidalwaveform in cut mode, which is best suited for dissecting tissue, and a25% duty cycle waveform in coagulation mode, which is best used forcauterizing tissue to stop bleeding.

The controller 24 includes a microprocessor 25 operably connected to amemory 26 that may be volatile type memory (e.g., RAM) and/ornon-volatile type memory (e.g., flash media, disk media, etc.). Themicroprocessor 25 includes an output port that is operably connected tothe HVPS 27 and/or the RF output stage 28 allowing the microprocessor 25to control the output of the generator 20 according to either openand/or closed control loop schemes.

A closed loop control scheme is a feedback control loop wherein thesensor circuitry 22, which may include a plurality of sensors measuringa variety of tissue and energy properties (e.g., tissue impedance,tissue temperature, output current and/or voltage, etc.), providesfeedback to the controller 24. The controller 24 then signals the HVPS27 and/or RF output stage 28 which then adjusts the DC and/or the RFpower supply, respectively. The controller 24 also receives inputsignals from the input controls of the generator 20 or the instrument10. The controller 24 utilizes the input signals to adjust poweroutputted by the generator 20 and/or perform other control functionsthereon.

The DC blocking capacitor 29 provides DC blocking for electrosurgicalenergy going to an active electrode (not shown). The measuring circuit30 measures the voltage across the DC blocking capacitor 29 forcommunication to the sensor circuit 21. The DC blocking capacitor 31provides DC blocking of return electrosurgical energy. The measuringcircuit 32 measures the voltage across the DC blocking capacitor 31. Thesensor circuit 32 can determine the current of the electrosurgicalenergy supplied to the active electrode utilizing the voltage acrosscapacitor 29 and likewise can determine the return current utilizing thevoltage across DC blocking capacitor 31. The controller 24 can utilizethe voltages and/or the currents through DC blocking capacitors 29 or 31to detect any faults therein.

The current communicated through DC blocking capacitors 29 or 31 can bedetermined using voltage measurements obtained from the measuringcircuits 30 or 32, respectively. The current through a capacitor may bedetermined using its voltage by using the following relation (I):

I=C(dv/dt),  (1)

where C is an estimated capacitance of the DC blocking capacitor, dv isthe measure of the voltage across the DC blocking capacitor, and dt is apredetermined interval of the electrosurgical energy. The predeterminedinterval may be the switching interval of the electrosurgical energy.

The sensor circuit 21 communicates the currents to cut-off circuit 22and/or controller 24. The cut-off circuit 22 can compare the outputcurrent to a reference. (e.g., using comparator 34). If the outputcurrent exceeds the reference, then the cut-off circuit 22 signals theswitch 33 to disconnect the RF output stage from the active electrode(not shown). The leakage current measuring circuit 23 receives theelectrosurgical current and return current from the leakage currentmeasuring circuit 23. The leakage current measuring circuit 23determines the leakage current for communication to the controller 24.

FIG. 3 shows a circuit coupled to a DC blocking capacitor 35 that may beused by the generator of FIG. 1 and/or 2 according to the presentdisclosure. FIG. 3 shows the DC blocking capacitor 35 which may beblocking capacitor 29 and/or 31 of FIG. 2. The capacitors 36, 37, 38,and 39 are arranged in an H configuration and function as a dividernetwork. The capacitors 36, 37, 38, and 39 provide an isolation barrierbetween the patient and the ground of the generator. In some embodimentsof the present disclosure, optocouplers and/or isolation transformersare used to provide an isolation barrier between the patient and theground of the generator; and in other embodiments they are not used. Themeasuring circuit 40 may be measuring circuit 30 or 32 of FIG. 2. Themeasuring circuit 40 measures the voltage difference between the nodesof: (1) the node between capacitors 36 and 38, and (2) the node betweencapacitors 37 and 39. The capacitors 36 and/or 37 may be split intovarious parallel or serial capacitors to adjust creepage, clearance, andthe voltage breakdown for the isolation barrier between the patient andground. The capacitors 36 and 38 form a divider network. The capacitors37 and 39 form another divider network. The capacitors 36 and 37 havethe same capacitance; and the capacitors 38 and 39 have the samecapacitance. The divider network formed by capacitors 36, 37, 38, and 39reduces the voltage measured by measuring circuit 40 by a predeterminedamount and is a function of the frequency of the electrosurgical energy,the capacitance of the capacitors 36, 37, 38 and 39, and the DC blockingcapacitor 35. The capacitors 36, 37, 38, and 39 are sufficient toprovide isolation between a ground of the electrosurgical generator 20(See FIG. 1) and the patient P, e.g., to prevent voltage breakdown ofthe capacitors 36, 37, 38, and 39 during typical use between the patientand a ground of the electrosurgical generator 20.

In some embodiments of the present disclose, a transformer may beinterposed between DC blocking capacitor 35 and measuring circuit 40 toprovide isolation therebetween and/or to step-down the voltage of theelectrosurgical energy prior to measurement by measuring circuit 40.

FIG. 4 shows a circuit 400 coupled to a DC blocking capacitor 35 a and aredundant DC blocking capacitor 35 b for determining the current of theelectrosurgical energy according to the present disclosure. Nodes 402and 404 may be coupled between SWT 33 of FIG. 2 and the active electrode(not shown). For example, the blocking capacitors 35 a and 35 b may beused in place of or in addition to capacitor 29 of FIG. 2. The circuit400 includes the measuring circuits 40 a and 40 b. The measuring circuit40 a measures the voltage across the DC blocking capacitor 35 a usingthe capacitors 36 a, 37 a, 38 a and 39 a. The measuring circuit 40 bmeasures the voltage across the DC blocking capacitor 35 a using thecapacitors 36 a, 37 a, 38 a, and 39 a. The blocking capacitors 35 a and35 b provide redundant electrosurgical energy measurements.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

1. An electrosurgical system comprising: an electrosurgical instrumentincluding at least one active electrode adapted to apply electrosurgicalenergy to tissue; and an electrosurgical generator adapted to supply theelectrosurgical energy to the at least one active electrode, theelectrosurgical generator comprising: an RF output stage adapted togenerate the electrosurgical energy; a DC blocking capacitorelectrically coupled between the RF output stage and tissue; a measuringcircuit coupled to the DC blocking capacitor to measure a voltage acrossthe DC blocking capacitor; and a sensor circuit to determine the currentof the electrosurgical energy as a function of the voltage across the DCblocking capacitor.
 2. The electrosurgical system according to claim 1,further comprising: a first capacitor having a first node coupled afirst node of the DC blocking capacitor; a second capacitor having afirst node coupled between a second node of the first capacitor and areference; a third capacitor having a first node coupled to a secondnode of the DC blocking capacitor; and a fourth capacitor having a firstnode coupled between a second node of the third capacitor and thereference; wherein the sensor circuit is coupled to the second node ofthe first capacitor and the second node of the third capacitor todetermine the voltage therebetween to determine the current of theelectrosurgical energy as the function of the voltage across the DCblocking capacitor.
 3. The electrosurgical system according to claim 2,wherein the first capacitor has a capacitance that is about equal to acapacitance of the third capacitor.
 4. The electrosurgical systemaccording to claim 3, wherein the second capacitor has a capacitancethat is about equal to a capacitance of the fourth capacitor.
 5. Theelectrosurgical system according to claim 1, wherein the sensor circuitdetermines the current utilizing the relationship of:I=C(dv/dt), wherein C is an estimated capacitance of the DC blockingcapacitor, dv is the measure of the voltage across the DC blockingcapacitor, and dt is a predetermined interval of the electrosurgicalenergy.
 6. The electrosurgical system according to claim 1, wherein theDC blocking capacitor has a capacitance of about 50 nF.
 7. Theelectrosurgical system according to claim 1, wherein the DC blockingcapacitor has a capacitance of about 5 nF.
 8. The electrosurgical systemaccording to claim 1, wherein the electrosurgical system determines thecurrent of the electrosurgical energy in an absence of a current sensetransformer to measure the current of the electrosurgical energy.
 9. Anelectrosurgical generator comprising: an RF output stage adapted togenerate electrosurgical energy for application to an active electrode;a DC blocking capacitor electrically coupled between the RF output stageand the active electrode; a measuring circuit coupled to the DC blockingcapacitor to measure a voltage across the DC blocking capacitor; and asensor circuit to determine the current of the electrosurgical energy asa function of the voltage across the DC blocking capacitor.
 10. Theelectrosurgical generator according to claim 9, further comprising: afirst capacitor having a first node coupled a first node of the DCblocking capacitor; a second capacitor having a first node coupledbetween a second node of the first capacitor and a reference; a thirdcapacitor having a first node coupled to a second node of the DCblocking capacitor; and a fourth capacitor having a first node coupledbetween a second node of the third capacitor and the reference; whereinthe sensor circuit is coupled to the second node of the first capacitorand the second node of the third capacitor to determine the voltagetherebetween to determine the current of the electrosurgical energy asthe function of the voltage across the DC blocking capacitor.
 11. Theelectrosurgical generator according to claim 10, wherein the first,second, third, and fourth capacitors are sufficient to provide isolationbetween a ground of the electrosurgical generator and a patient.
 12. Theelectrosurgical generator according to claim 10, wherein the firstcapacitor has a capacitance that is about equal to a capacitance of thethird capacitor.
 13. The electrosurgical generator according to claim12, wherein the second capacitor has a capacitance that is about equalto a capacitance of the fourth capacitor.
 14. The electrosurgicalgenerator according to claim 9, wherein the sensor circuit determinesthe current utilizing the relationship of:I=C(dv/dt), wherein C is an estimated capacitance of the DC blockingcapacitor, dv is the measure of the voltage across the DC blockingcapacitor, and dt is a predetermined interval of the electrosurgicalenergy.
 15. The electrosurgical generator according to claim 9, whereinthe DC blocking capacitor has a capacitance of one of about 50 nF andabout 5 nF.
 16. The electrosurgical generator according to claim 9,wherein the electrosurgical system determines the current of theelectrosurgical energy in an absence of a current sense transformer tomeasure the current of the electrosurgical energy.
 17. Theelectrosurgical generator according to claim 9, further comprising: afifth capacitor connected in one of in series or in parallel to thefirst capacitor; and a sixth capacitor connected in one of in series orin parallel to the third capacitor.
 18. The electrosurgical generatoraccording to claim 9, further comprising a cut-off circuit coupled tothe sensor circuit to communicate the determined current of theelectrosurgical therefrom, wherein the cut-off circuit is adapted tostop the application of the electrosurgical energy to the activeelectrode when the measured current reaches a predetermined threshold.19. The electrosurgical generator according to claim 18, furthercomprising a switch coupled to between the RF output stage and theactive electrode, wherein the cut-off circuit includes a comparator tocompare the determined current to the predetermined threshold and togenerate a cut-off signal adapted to signal the switch to stop theapplication of the electrosurgical energy to the active electrode. 20.The electrosurgical generator according to claim 9, further comprising:a return electrode adapted to return the electrosurgical energy; anotherDC blocking capacitor electrically coupled between the RF output stageand a return electrode adapted to return the electrosurgical energy fromtissue; an another measuring circuit coupled to the another DC blockingcapacitor to measure the voltage across the another DC blockingcapacitor; wherein the sensor circuit determines the current of thereturn electrosurgical energy as a function of the voltage across theanother DC blocking capacitor; and a leakage current measuring circuitcoupled to the sensor to compare the current of the electrosurgicalenergy to the current of the return electrosurgical energy to measure aleakage current.
 21. The electrosurgical generator according to claim 9,further comprising a redundant DC blocking capacitor coupled in serieswith the DC blocking capacitor, wherein the sensor circuit determinesthe current of the electrosurgical energy as a function of the voltageacross the redundant DC blocking capacitor.